Zirconium alloy



United States Patent ,68 Int. Cl. CZZc 15/00, 1/04 US. Cl. 75-177 6 Claims ABSTRACT OF THE DISCLOSURE A zirconium-base alloy resistant to corrosion contains 0.5 to 6% by weight of copper and at least one additive of magnesium, platinum or manganese in amounts from 0.1 to 5%, the balance being zirconium of nuclear purity.

This invention relates to zirconium alloys and more specifically at leastv to the ternary alloys which have a high zirconium content. One important application of alloys of this type lies in the development of structural materials for use in nuclear reactors of the type which are cooled by circulation of carbon dioxide gas under pressure.

The utilization of zirconium-base alloys containing copper for the fabrication of construction materials employed in pressurized carbon-dioxide gas cooled reactors has already been contemplated. The presence of copper endows zirconium-copper alloys with corrosion resistance which is superior to that of pure zirconium, especially in a moist carbon dioxide atmosphere.

This invention is directed to the production of at least a ternary alloy having a zirconium base and containing copper which meets practical requirements more effectively than the alloys which were hitherto employed in the prior art, especially insofar as it has higher mechanical strength and improved creep strength at high temperature.

Accordingly, the invention proposes a zirconium-base alloy which contains between 0.5 and 6% by weight of copper, characterized in that it comprises a total of 0.1 to 5% of at least one of the additives of the group constituted by magnesium, cerium, platinum and manganese (the proportion of cerium being at least 1% if it constitutes the sole additive), the remainder being nuclear pure zirconium.

A noteworthy result thereby achieved is that, at a temperature of 500 to 600 C. and at a pressure varying between 25 and 60 bars, the strength of the alloy which is thus obtained is considerably greater than that of zirconium in the carbon dioxide gas which is commonly employed as coolant in nuclear reactors.

The different impurities contained in the alloy, and in particular aluminum, titanium and silicon, must be present in as low a proportion as possible in order not to reduce the corrosion resistance of the alloy. In practice, the maximum proportions of aluminum, titanium and silicon which are present in the starting zirconium must be 0.01% by Weight in each case.

Furthermore, if the alloy is intended to constitute structural elements which are placed in the neutron flux of a nuclear eactor, the zirconium which is employed for the fabrication of the alloy must be dehafniated; by .dehafniated zirconium is meant zirconium which contains a sufficiently low proportion of hafnium to prevent any appreciable increase in the neutron capture cross-section of the zirconium alloy. This is explained by the fact that hafnium has a high thermal-neutron cross-section and would thus have an unfavorable influence on the neutron characteristics of structural materials. Practically speaking, zirconium can be considered as hafnium-free or dehafniated when its hafnium content does not exceed 0.02% by weight.

The best solution consists in utilizing as starting product in the fabrication of the alloy the so-called nuclear pure zirconium (reactor grade zirconium) which contains the following maximum percentages by weight of impurities.

Zirconium Zirconium Element sponge Element sponge Copper 1.5-2.5 Mg 0.5-1 Pt 0.2

The alloy compositions which are defined hereinabove have properties which permit of their use as structural materials (fuel element cans, especially ceramic materials such as U0 guide tubing and the like) in nuclear reactors which are cooled by circulation of carbon dioxide gas under pressure.

The preparation of the alloy can be carried out by means of a number of different processes. It is possible in particular to employ nuclear pure zirconium sponge as starting material, to comminute the metal until granular particles are obtained and to distribute the copper and the other additive or additives in suitable proportions in the mass of granular material (the proportion of additive which is thus incorporated may be dependent on the quantities introduced by the zirconium). The mixture of granular material, copper and the other additive or additives is then compacted to form rods 30 mm. in diameter which are then melted in an electric furnace with a consumable electrode in a vacuum of the order of 10- mm. of mercury. The alloy ingots resulting from the initial melt are then re-melted in the electric furnace which is equipped with a consumable electrode and produce homogeneous ingots mm. in diameter which are readily adaptable to subsequent conversion processes.

The corrosion resistance of the alloys defined above has been determined by their weight gain as compared with that of high-purity zirconium when the two metals are placed in a same carbon dioxide gas atmosphere for a predetermined length of time, at a predetermined temperature and pressure:

EXAMPLE 1 A specimen of high-purity zirconium and a specimen of alloy containing 2.5% by weight of copper and 0.5% by weight of magnesium were placed in a carbon dioxide gas atmosphere containing 20 volumes per million of water vapor. At 600 C. and at a pressure of 60 bars, the weight gains reached after 800 hours were 4.20 mg./cm. of surface area in the case of unalloyed zirconium and 3.71 mg./cm. in the case of the alloy hereinabove defined; after 2,500 hours, the weight gains were 10.9 mg./

cm. in the case of unalloyed zirconium and this latter had undergone breakaway; on the contrary, the alloy had only shown a gain of 4.9 mg./cm.

EXAMPLE 2 EXAMPLE 3 Under the same conditions as those mentioned above, the following weight gains were obtained after 1,000 hours:

4.6 mg./cm. in the case of zirconium, 3.9 mg./cm. in the case of an alloy containing 2.5%

Cu and 0.3% Mn.

We claim:

1. A zirconium-base alloy consisting essentially of 0.5 to 6% by weight of copper, 0.1 to 5% of at least one of the additives of the group consisting of magnesium, platinum and manganese, the balance being zirconium of nuclear purity.

2. A zirconium-base alloy consisting essentially of 1.5 to 2.5 by weight of copper and 0.5 to 1% of magnesium, the balance being zirconium.

3. A zirconium-base alloy consisting essentially of 1.5 to 2.5 by weight of copper and approximately 0.2% of platinum, the balance being zirconium.

4. An alloy in accordance with claim 1, consisting essentially of 1.5 to 2.5 by weight of copper and 0.3 to 1% of manganese, the balance being zirconium.

5. An alloy in accordance with claim 1, wherein aluminium, titanium and silicon in the alloy with respect to zirconium correspond to a maximum of 0.01% each.

6. A structural material for use in a nuclear reactor cooled by carbon dioxide at a maximum temperature between 500 and 600 C., of the alloy of claim 1.

References Cited UNITED STATES PATENTS 3,261,582 7/1966 Rosler 75177 FOREIGN PATENTS 1,344,069 10/1963 France.

CHARLES N. LOVELL, Primary Examiner US. Cl. X.R. 176-88, 91 

